1. Field of the Invention
The present invention relates to an integrated circuit and to a method for generating a ready signal which, after a power supply of an integrated circuit has been connected, indicates that the supply voltage is high enough for performing functions of the integrated circuit faultlessly.
2. Description of the Related Art
Nowadays, a circuit for detecting the adequate supply voltage is built into almost every complex chip or almost every complex integrated circuit, respectively. In particular, an appropriate logic ensures that when a power supply for the integrated circuit is switched on, after a certain level of the supply voltage is reached, an internal reset signal or an initialization signal is generated for a certain period of time which effects a resetting or initialization of the entire digital logic or also analog circuit. In this arrangement, the supply voltage is usually detected by a detection circuit which makes use of the turn-on voltage of an n- or p-channel transistor. When the turn-on voltage is reached, the reset or initialization signal is activated for a certain period of time and then deactivated again. The reset or initialization signal is generally referred to herein as the ready signal in the text which follows.
In a conventional integrated circuit, it is possible, when the supply voltage rises very slowly, that the ready signal is generated at a time at which the supply voltage is not yet high enough for the integrated circuit to be correctly reset or initialized. Furthermore, it is possible, when the supply voltage rises very slowly, that after the resetting or initialization, the supply voltage is not yet high enough for keeping all analog circuit blocks or part-circuits of the integrated circuit in a settled state. For example, part-circuits which need voltage generators or obtain input voltages from these can then start at a supply voltage which is too low. In this case, it is not ensured that the resetting or initialization, also called power-on sequence in the text which follows, proceeds correctly. For example, at a node which is provided for being supplied with a negative voltage by a voltage generator, a positive voltage can form for a short time. In general, unwanted states can occur which cast doubt on a correct resetting or a correct initialization, and thus on a correct operation overall.
Another disadvantage of conventional circuits is that power-on detection circuits in some cases need high currents which are not compatible with a low-power design or a design for low-power consumption, respectively.
Thus, there is a need for an improved integrated circuit or an improved method for generating a ready signal which indicates that the supply voltage of an integrated circuit is high enough.